CHAPTER XI.

THE STARS AND NEBULE.

UNTIL lately the attention of astronomers was almost exclusively directed to the solar system; the sidereal heavens were regarded as a mere assemblage of fixed stars, so unchanging in their appearance and unvaried in their character as to possess very little interest. Since the days of Sir William Herschel, however, this department of astronomy has yielded far more magnificent results than the most imaginative philosopher had ever dreamed of.

We now know that the visible universe is composed, not of single stars, as we might imagine from looking up into the heavens, just as a man who has spent his life in a city might suppose the whole world to be filled with streets. The true denizens of heaven are small faint spots of light called nebulæ, scattered through space, and placed at such inconceivable distances, that light must travel a thousand years before it can pass from one to another.

These little faint spots of light, when magnified by the telescope, present strange and unimagined forms, which require to be pictured rather than described. For this reason we prefer presenting our readers with portraits of a number of them, rather than attempt a profitless description. We merely observe, that of those which we have

selected for delineation, the most prevailing forms are those of the circular and annular nebula.

Our best

And what, it will be asked, are these nebula of which the visible universe is said to be composed? answer is to select one of them, and go to see it. For this purpose we will choose No. 1, which at a great distance seems to be no more than a faint spot of light in the midnight sky, but as we near it we find it growing in size and brightness, until it has covered nearly half the heavens, spreading a faint glow of light where formerly there was only gloom. Onwards we go towards its very centre, and now we can see minute points of light, like star dust sprinkled over the sky. Still we proceed on our ethereal voyage, and the little points of light increase in distinctness and brilliancy until we discover that they are really stars. At first they appeared as if they were all close to one another, now they recede and separate, and at last, when we have arrived near the centre of the nebula, we find the whole heavens glittering above, beneath, and around us with a panorama of magnificent stars. outer skirts of the nebula, however, are still very distant, and therefore still preserve their cloudy appearance, forming, as it were, a broad but irregular zone, that girdles the whole heavens, and that is called "The Galaxy, or Milky Way." Yes! it is quite true-almost the whole scenery that presents itself to our eyes upon a cloudless night is nothing more and nothing less than the spangled interior of one of these same nebulæ. Our sun is but one of the stars situated near the centre of this mighty system, which stretches out into the dim distance; and it is only the stars of that nebula in our immediate vicinity that sparkle singly in the breast of night.

The

It is to this latter class that we would now turn our

attention, in order to notice some remarkable phenomena connected with them. As might be expected, these stars vary in brightness, not only according to their size, but also according to their distance. Some of them, probably, are smaller than our sun; others of them, such as Sirius and Arcturus, we know to be larger. Their distance is so inconceivably great, that light requires upwards of three years to travel from the nearest of them; and if this be the case with the nearest, imagination fails in its attempts to conceive the distance of the others.

These stars, of course, shine by their own light, and are therefore in reality suns. Many, if not all of them, must have planets revolving round them, and receiving both light and heat from their radiance. That there is abundance of variety in their constitutions is evident, not only from their difference in colour, but also from some of them being double. Stars that appear to the naked eye as one, are found, on the application of the telescope, to be composed of two stars, some, of three, and others, of a greater number. Observation has proved that these double and triple stars are continually changing their relative positions; and, in regard to many of them, it has been ascertained that they revolve the one around the other, or around a common centre. When viewed through the telescope, these double stars appear as if the suns of which they are composed were very near each other. This, however, is not the case; the orbit of Neptune would be too small to indicate their distance; in many cases it must be a thousand times greater. Their planetary systems, therefore, will be in no danger of coming into collision, and even the perturbations of their planets by the companion sun will not be very observable.

A remarkable circumstance connected with these

double stars is, that in many instances they not only differ in colour, but, strange to say, the colour of the one is generally the complement or contrast of the other. For example, if the brighter of the two be red, its companion is generally inclined to be of a greenish hue. This difference of colour, which is so well marked in many of the stars visible to the naked eye, and still more in the double stars, seems to indicate a difference in the colour of the flame caused by the combustion of different kinds of meteoric fuel. Thus Arcturus, Aldebaran, Pollux, and Antares are reddish in their colour; Sirius, Deneb, Vega, and Regulus are white; Procyon, Atair, the Pole-star, and Beta of Ursa Major, are yellow; while Castor is observed to have a greenish tint. It is probable that in the case of the white stars, the want of any colour is due to the equal quantities of meteoric matter producing coloured flames of opposite tints, and that where the colour is decided there is a preponderance of a certain kind of fuel. Probably in the double stars one may attract one kind of substance, and the other another kind, and hence the opposition of their tints; but in any case we may safely infer that the difference of colour must be due to the chemical qualities of the fuel.

If this be the case, it is clearly not impossible but that, by means of the prismatic spectrum, we may yet obtain important information regarding the chemical nature of the substances of which each star is composed. When, by means of a prism, we analyse the light of any flame, we find a great variety in the patterns of the different spectra, even when their colours are not perceptibly different. Not only is there a different gradation of tints, there are also lines of different colours which appear in different parts of the spectrum, by which we can classify the